1. Field of the Invention
The invention relates to the field of objective designation by laser guidance for weapons systems, and the subject, more particularly, is a device for monitoring of the alignment of two optical paths of a laser designation system or "pod" (this term signifying a nacelle in English) for target designation by laser guidance, namely an infrared optical path (of wavelengths from 8 to 12 micrometers) and a laser path (1 to 2 micrometers), and a laser designation system equipped with such a monitoring device.
2. Discussion of the Background
In severe environmental conditions, especially in terms of temperature and of vibration, target designation by laser guidance of the projectile is advantageously carried out by virtue of a "pod" arranged for external carriage on an aircraft and comprising an imaging path with infrared detection making it possible to locate the target and a laser path "locked" onto the imaging path. This locking assumes perfect alignment between the two paths, that is to say perfect parallelism of their optical axes thus defining the game aiming line. In fact this harmonization, carried out on a test bench in a factory, must be able to be monitored in the course of the mission.
In order to align the optical axes of a laser and of an infrared detector of an opto-electronic target designation system, U.S. Pat. No. 4,422,758 employs, as illustrated in FIG. 1, an optical device composed of mirrors 1 to 5. This device is intended to focus the laser beam FL onto refractory ceramics 6 in order to create a hot point thereon and to collimate the infrared radiation FI given off by this hot point onto the imaging path. The position of the image of the hot point on the imaging path makes it possible to measure the alignment errors of the two paths.
A first major drawback of this solution resides in the type of material used to implement it, namely refractory ceramics: this material exhibits low remanence an heats up neither easily nor quickly, which necessitates the focusing of significant energy onto the ceramics. These conditions of use render it difficult to implement due to:
--the pulse nature of the laser beam, necessitating luminosity remanence between two pulses;
--the employment, in thermal scanning cameras, of a system of deflection of the aiming line addressing the mosaic of detectors only for a very short time;
--and the duration of the alignment test, which must not exceed several seconds although the material used heats up with difficulty.
Another major drawback results from the errors in parallelism between the laser and infrared paths generated by inclination errors in the supports of the mirrors of the optical device; in order to resolve this problem, the prior art proposes a method of adjustment on the ground in three steps, particularly by making use of a telescope. Such an adjustment is fragile and cannot be preserved in the stressful conditions described.
A final drawback relates to the organization of the mirrors 1 to 5 of the optical system which confers a bulk on the assembly which is in fact incompatible with the space available.